Set of masks, method of generating mask data and method for forming a pattern

ABSTRACT

A method of generating mask data, for a set of masks used to transfer a pattern for delineating a circuit pattern of a semiconductor integrated circuit, includes preparing design data having a design pattern corresponding to the pattern to be transferred on a semiconductor substrate; generating resized data by enlarging the design data by a resizing quantity; generating first mask data by filling a space area having a space width of a space quantity or less of the resized data; and generating second mask data, to be aligned with the first mask data, having a window portion for selectively exposing an area determined by enlarging the space area by the resizing quantity.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. patent application Ser. No. 12/010,933, filed Jan. 31, 2008 now U.S. Pat. No 8,091,046, which is a divisional application of U.S. patent application Ser. No. 10/808,299, filed Mar. 25, 2004 (now U.S. Pat. No. 7,350,181 B2 issued Mar. 25, 2008), all of which are incorporated herein by reference.

This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. P2003-086563, filed on Mar. 26, 2003; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to technology of manufacturing a semiconductor device. More especially, this invention relates to a set of masks, a method of generating mask data and a method for forming a pattern.

2. Description of the Related Art

In recent years, with the trend toward higher integration of large scale integrated circuits (LSIs), there has been a demand for finer circuit patterns of LSIs. As examples, for a transistor in a microprocessing unit (MPU), an application specific integrated circuit (ASIC), a system LSI, or the like, there is a demanded for a pattern to be delineated with fine line widths of 100 nm or less.

As a method for forming a pattern with fine line widths, there is a known method in which a resist pattern with fine line widths is formed using a positive alternating phase shift mask (Levenson-type phase shift mask) where phase contrasts of adjacent openings are shifted from each other by 180 degrees, and any unnecessary part of the resist pattern is removed using a trim mask. Moreover, as another method for forming a pattern with fine line widths, a method has been studied in which isotropic etching is performed after the formation of a resist pattern, thereby slimming the line widths of the resist pattern.

Here, for example, as to a pattern of a memory cell of a SRAM or the like which coexists with a logic circuit, demand for the pattern have fine space widths in addition to fine line widths in order to reduce the circuit space. In the case of using a positive alternating phase shift mask (Levenson-type phase shift mask), it is required to form fine space widths when a trim mask is used. However, the resolution of a trim mask is low, and it is therefore difficult to form fine space widths in a resist pattern. Moreover, in the case of performing isotropic etching after the formation of a resist pattern, the space widths between the lines of the resist pattern are increased when the line widths of the resist pattern are slimmed. Therefore, it is difficult to delineate a circuit pattern which has fine line widths and fine space widths at the same time.

SUMMARY OF THE INVENTION

A feature of the present invention inheres in a method of generating mask data for a set of masks used to transfer a pattern for delineating a circuit pattern of a semiconductor integrated circuit. The method includes preparing design data having a design pattern corresponding to the pattern to be transferred on a semiconductor substrate; generating resized data by enlarging the design data by a resizing quantity; generating first mask data by filling a space area having a space width of a space quantity or less of the resized data; and generating second mask data, to be aligned with the first mask data, having a window portion for selectively exposing an area determined by enlarging the space area by the resizing quantity.

Another feature of the present invention inheres in a method for forming a pattern including depositing a process-target film on a semiconductor substrate; depositing an underlying mask film on the process-target film; delineating a first resist film on the underlying mask film; delineating a first resist pattern by transferring a pattern of a first mask onto the first resist film; delineating an underlying mask pattern having narrower line width than a line width of the first resist pattern by removing a part of the underlying mask film; delineating a second resist film on the underlying mask pattern; delineating a second resist pattern having a window portion for exposing a part of the underlying mask pattern, by transferring a pattern of a second mask onto the second resist film; and removing a part of the underlying mask pattern selectively, using the second resist pattern as an etching mask.

Additional feature of the present invention inheres in a set of masks for forming thin line portion having a line width thinner than a minimum line width which can be optically resolved by a projection exposure system by slimming a line width of a pattern transferred on a semiconductor substrate. The set of masks includes a first mask having the thin line pattern for forming the thin line portion; and a second mask having a window portion for removing an unnecessary portion from a pattern transferred by the first mask.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an example of mask data generation system according to a first embodiment of the present invention.

FIG. 2 is a plane view showing an example of design data according to the first embodiment of the present invention.

FIG. 3 is a plane view showing an example of resized data according to the first embodiment of the present invention.

FIG. 4 is a plane view showing an example of first mask data according to the first embodiment of the present invention.

FIG. 5 is a plane view showing an example of second mask data according to the first embodiment of the present invention.

FIG. 6A is a plane view showing an example of the first mask data on which optical proximity correction is performed according to the first embodiment of the present invention.

FIG. 6B is a plane view showing an example of the second mask data on which optical proximity correction is performed according to the first embodiment of the present invention

FIG. 7 is a flowchart for explaining an example of a method of generating mask data according to the first embodiment of the present invention.

FIG. 8A is a plane view showing an example of a first mask of a set of masks according to the first embodiment of the present invention.

FIG. 8B is a sectional view at A-A shown in FIG. 8A.

FIG. 9A is a plane view showing an example of a second mask of the set of masks according to the first embodiment of the present invention.

FIG. 9B is a sectional view at A-A at FIG. 9A.

FIG. 10 is a plane view for explaining alignment between a first mask pattern and a second mask pattern of the set of masks according to the first embodiment of the present invention.

FIG. 11 is a sectional view for explaining a method for forming pattern according to the first embodiment of the present invention.

FIG. 12A is a plane view in process after process shown in FIG. 11 for explaining an example of a method for forming a pattern according to the first embodiment of the present invention.

FIG. 12B is a sectional view at A-A shown in FIG. 12A.

FIG. 13A is a plane view in process after process shown in FIG. 12A for explaining an example of a method for forming a pattern according to the first embodiment of the present invention.

FIG. 13B is a sectional view at A-A shown in FIG. 13A.

FIGS. 14 and 15 are sectional views in processes after process shown in FIG. 13B for explaining an example of a method for forming a pattern according to the first embodiment of the present invention.

FIG. 16A is a plane view in process after process shown in FIG. 15 for explaining an example of a method for forming a pattern according to the first embodiment of the present invention.

FIG. 16B is a sectional view at B-B shown in FIG. 16A.

FIGS. 17 and 18 are sectional views in processes after process shown in FIG. 16B for explaining an example of a method for forming a pattern according to the first embodiment of the present invention.

FIG. 19A is a plane view in process after process shown in FIG. 18 for explaining an example of a method for forming a pattern according to the first embodiment of the present invention.

FIG. 19B is a sectional view at B-B shown in FIG. 19A.

FIG. 20 is a sectional view for explaining an example of a method for forming a pattern according to a first modification of the first embodiment of the present invention.

FIGS. 21 and 22 are sectional views for explaining an example of a method for forming a pattern according to a second modification of the first embodiment of the present invention.

FIG. 23 is a block diagram showing an example of mask data generation system according to a second embodiment of the present invention.

FIG. 24 is a schematic view showing an example of design data according to the second embodiment of the present invention.

FIG. 25 is a schematic view showing an example of a resized data according to the second embodiment of the present invention.

FIG. 26 is a schematic view is a schematic view showing an example of first mask data according to the second embodiment of the present invention.

FIG. 27 is a schematic view showing an example of second mask data according to the second embodiment of the present invention.

FIG. 28 is a schematic view showing an example of second mask data having a window portion is enlarged according to the second embodiment of the present invention.

FIG. 29A is a schematic view showing an example of first mask data on which optical proximity correction is performed according to the second embodiment of the present invention.

FIG. 29B is a schematic view showing an example of second mask data on which optical proximity correction is performed according to the second embodiment of the present invention.

FIG. 30 is a flowchart for explaining an example of a method of generating mask data according to the second embodiment of the present invention.

FIG. 31 is a plane view showing an example of a first mask of a set of masks according to the second embodiment of the present invention.

FIG. 32 is a plane view showing an example of a second mask of the set of masks according to the second embodiment of the present invention.

FIG. 33 is a plane view for explaining alignment between a first mask pattern and a second mask pattern of the set of mask according to the second embodiment of the present invention.

FIG. 34A is a plane view for explaining an example of a method for forming a pattern according to the second embodiment of the present invention.

FIG. 34B is a sectional view at A-A shown in FIG. 34A.

FIG. 35A is a plane view in process after process shown in FIG. 34A for explaining an example of a method for forming a pattern according to the first embodiment of the present invention.

FIG. 35B is a sectional view at A-A shown in FIG. 35A.

FIG. 36 is sectional view in process after process shown in of FIG. 35B for explaining an example of a method for forming a pattern according to the second embodiment of the present invention.

FIG. 37A is a plane view in process after process shown in of FIG. 36 for explaining an example of a method for forming a pattern according to the second embodiment of the present invention.

FIG. 37B is a sectional view at B-B shown in FIG. 37A.

FIGS. 38 and 39 are sectional views in processes after process shown in of FIG. 37B for explaining an example of a method for forming a pattern according to the second embodiment of the present invention.

FIG. 40A is a plane view in process after process shown in FIG. 39 for explaining an example of a method for forming a pattern according to the second embodiment of the present invention.

FIG. 40B is a sectional view at B-B shown in FIG. 40A.

FIGS. 41 and 42 is sectional views in processes after process shown in of FIG. 40B for explaining an example of a method for forming a pattern according to the second embodiment of the present invention.

FIG. 43A is a plane view in process after process shown in of FIG. 42 for explaining an example of a method for forming a pattern according to the first embodiment of the present invention.

FIG. 43B is a sectional view at B-B shown in FIG. 43A.

FIG. 44A is a plane view for explaining an example of a method for forming a pattern according to a first modification of the first embodiment of the present invention.

FIG. 44B is a sectional view at B-B shown in FIG. 44A.

FIG. 45 is sectional view for explaining an example of a method for forming a pattern according to the first modification of the first embodiment of the present invention.

FIGS. 46 to 50 are sectional views for explaining an example of a method for forming a pattern according to a second modification of the first embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that the same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the description of the same or similar parts and elements will be omitted or simplified.

Generally and as it is conventional in the representation of LSI, it will be appreciated that the various drawings are not drawn to scale from one figure to another nor inside a given figure, and in particular that the layer thicknesses are arbitrarily drawn for facilitating the reading of the drawings.

(First Embodiment)

As shown in FIG. 1, a mask data generation system according to a first embodiment of the present invention includes a central processing unit (CPU) 1, design data storage device 2, a process condition storage device 3, a resizing quantity storage device 4, a space quantity storage device 5, a mask data storage device 6, a main memory 7, an input device 8, and an output device 9.

The process condition storage device 3 stores process conditions, such as exposure conditions and ion implantation conditions, for delineating a circuit pattern of a semiconductor integrated circuit (IC). Here, exposure conditions also include a minimum line width and a minimum space width with which a pattern can be optically resolved by a projection exposure system used in the photolithography processes, as an example.

The design data storage device 2 stores in advance design data. The design data is drawn design patterns that correspond to patterns having desired shapes on a semiconductor substrate for delineating the circuit patterns of the semiconductor IC. For example, as shown in FIG. 2, design data 110 includes four design patterns 110 a, 110 b, 110 c, and 110 d, all of which have line symmetrical (mirror symmetrical) relationships of with one another. The design patterns 110 a, 110 b, 110 c, and 110 d include stripe-shaped thin line portions 112 a, 112 b, 112 c, and 112 d, respectively, and rectangular portions 111 a, 111 b, 111 c, and 111 d, respectively, each of which has a substantially square shape and is connected with an outer end portion of the corresponding thin line portion 112 a, 112 b, 112 c, or 112 d.

The two thin line portions 112 a and 112 b are separated from each other by a space width S_(d0) therebetween in the X-axis direction and arranged with a line width W_(d0) along a single line. The line width W_(d0) is, for example, the minimum line width in the design data 110 and may be smaller than a minimum line width with which a pattern can be optically resolved by a projection exposure system used in the photolithography processes. The two thin line portions 112 c and 112 d are also separated from each other by the space width S_(d0) therebetween in the X-axis direction and arranged with the line width W_(d0) along another single line. The two thin line portions 112 a and 112 c are separated from each other in parallel by a space width S_(d1) therebetween in the Y-axis direction. The two thin line portions 112 b and 112 d are also separated from each other in parallel by the space width S_(d1) therebetween in the Y-axis direction. Moreover, the two rectangular portions 111 a and 111 c are separated from each other by a space width S_(d0) therebetween in the Y-axis direction. The two rectangular portions 111 b and 111 d are also separated from each other by the space width S_(d0) therebetween in the Y-axis direction.

Note that the design data 110 is designed based on design rules of circuit patterns of semiconductor ICs. The design rules may be stored in the design data storage device 2 shown in FIG. 1. The design rules can be appropriately determined based on the process conditions stored in the process condition storage device 3, and the like.

The resizing quantity storage device 4 stores, as a “resizing quantity ” a predetermined dimension that is larger than a half value of a difference between the minimum line width with which a pattern can be optically resolved by a projection exposure system used in the photolithography processes, and the minimum line width of the design pattern drawn in the design data. The resizing quantity ΔD₁ can be appropriately determined in a range which satisfies the following expression (1): ΔD ₁≧(W _(min) −W _(d0))/2   (1) where W_(min) is the minimum line width with which a pattern can be optically resolved by a projection exposure system used in the photolithography processes, and W_(d0) is the minimum design line width in the design data.

The space quantity storage device 5 stores, as a “space quantity, ” a predetermined dimension that is larger than the minimum space width with which a pattern can be optically resolved by a projection exposure system used in the photolithography processes. Based on a line width reducing quantity or the like in an etching process, the space quantity ΔS can be appropriately determined in a range which satisfies the following expression (2): ΔS>S_(min)   (2) where S_(min) is the minimum space width with which a pattern can be optically resolved by a projection exposure system.

The CPU 1 includes a resized data generation module 1 a, a first mask data generation module 1 b, a second mask data generation module 1 c, and an optical proximity correction (OPC) module 1 e. The resized data generation module 1 a reads the design data stored in the design data storage device 2 and the resizing quantity ΔD₁ stored in the resizing quantity storage device 4, and generates resized data including a resized pattern by equally enlarging a design pattern in the design data by the resizing quantity. For example, as shown in FIG. 3, the resized data generation module 1 a generates resized data 120 including four resized patterns 120 a, 120 b, 120 c, and 120 d by equally enlarging the respective design patterns 110 a, 110 b, 110 c, and 110 d in the design data 110 shown in FIG. 2, each by the resizing quantity ΔD₁.

The four resized patterns 120 a, 120 b, 120 c, and 120 d have the same shapes and relationships of line symmetry with one another. The resized patterns 120 a, 120 b, 120 c, and 120 d include stripe-shaped thin line portions 122 a, 122 b, 122 c, and 122 d, respectively, and rectangular portions 121 a, 121 b, 121 c, and 121 d, respectively, each of which has a substantially square shape and is connected with an outer end portion of the corresponding thin line portion 122 a, 122 b, 122 c, or 122 d. The two thin line portions 122 a and 122 b are separated from each other by a space width S_(d2) therebetween in the X-axis direction and arranged with a line width W_(d1) along a single line in the X-axis direction. The line width W_(d1)is larger than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system used in the lithography processes. The space width S_(d2) is, for example, smaller than the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system. Moreover, the two thin line portions 122 c, and 122 d are also separated from each other by the space width S_(d2) therebetween in the X-axis direction and arranged with the line width W_(d1) along another single line in the X-axis direction.

The two thin line portions 122 a and 122 c are separated from each other in parallel by a space width S_(d3) therebetween in the Y-axis direction. The thin line portions 122 b and 122 d are also separated from each other in parallel by the space width S_(d3) therebetween in the Y-axis direction. Moreover, the rectangular portions 121 a and 121 c are separated from each other by the space width S_(d2) therebetween in the Y-axis direction. The rectangular portions 121 b and 121 d are also separated from each other by the space width S_(d2) therebetween in the Y-axis direction.

The first mask data generation module 1 b shown in FIG. 1 reads the resized data generated by the resized data generation module 1 a and the space quantity ΔS stored in the space quantity storage device 5, and generates first mask data by filling a space area, in the resized data, forming a space width smaller than the space quantity ΔS. For example, the first mask data generation module 1 b determines areas, each having the space width S_(d2), between the rectangular portions 121 a and 121 c between the rectangular portions 121 b and 121 d, between the thin line portions 122 a and 122 b, and between the thin line portions 122 c and 122 d, in the resized data 120 shown in FIG. 3, as space areas 123 a, 123 b, 123 c, and 123 d, respectively. Further, as shown in FIG. 4, the first mask data generation module 1 b generates first mask data 130 by filling each of the space areas 123 a, 123 b, 123 c, and 123 d shown in FIG. 3.

The first mask data 130 includes two thin line patterns 131 a and 131 b, and a pair of connection patterns 132 a and 132 b which sandwich the two thin line patterns 131 a and 131 b at both ends thereof and connect the line patterns 131 a and 131 b with each other. The two thin line patterns 131 a and 131 b are separated from each other by the space width S_(d3) therebetween in the Y-axis direction and arranged in parallel each with the line width W_(d1) in the X-axis direction. The interior area surrounded by the two thin line patterns 131 a and 131 b and the pair of connection patterns 132 a and 132 b serves as a window portion 133.

The second mask data generation module 1 c shown in FIG. 1 reads the resized data generated by the resized data generation module 1 b and the resizing quantity ΔD₁ stored in the resizing quantity storage device 4, and generates second mask data having a window portion for selectively exposing an area determined by enlarging the space area in the resized data by the resizing quantity ΔD₁. For example, as shown in FIG. 5, the second mask data generation module 1 c generates second mask data 150 having four window portions 151 a, 151 b, 151 c, and 151 d for selectively exposing areas which are obtained by enlarging the respective space areas 123 a, 123 b, 123 c, and 123 d in the resized data 120 shown in FIG. 3, each by the resizing quantity ΔD₁.

The second mask data 150 can be aligned with the first mask data 130 shown in FIG. 4. The two window portions 151 a and 151 b are patterns for selectively exposing parts of the connection patterns 132 a and 132 b with the space width S_(d0), at the positions of the space areas 123 a and 123 b, respectively. The two window portions 151 c and 151 d are also patterns for selectively exposing parts of the thin line patterns 131 a and 131 b with the space width S_(d0), at the positions of the space areas 123 c and 123 d, respectively.

The OPC module 1 d shown in FIG. 1 reads the first mask data generated by the first mask data generation module 1 b, the second mask data generated by the second mask data generation module 1 c, and an OPC quantity included in the exposure conditions stored in the process condition storage device 3. The OPC module 1 d then performs OPC on each of the first and second mask data so that each of the first and second mask data has a resist shape after exposure process.

For example, the OPC module 1 d performs OPC on the first mask data 130 shown in FIG. 4. As shown in FIG. 6A, the OPC module 1 d adds rectangular positive OPC patterns 143 a, 143 b, 143 c, and 143 d, as well as rectangular cut-out patterns (negative OPC patterns) 144 a and 144 b. The positive OPC patterns 143 a, 143 b, 143 c, and 143 d are partially superimposed on four outer corners of the connection patterns 132 a and 132 b. The negative OPC patterns 144 a and 144 b are partially superimposed on part of the two thin line patterns 131 a and 131 b and part of the connection patterns 132 a and 132 b each in a C-shape, in the vicinities of both ends of the window portion 133 in the X-axis direction. Moreover, the OPC module 1 d performs OPC on the second mask data 150 shown in FIG. 5. As shown in FIG. 6B, the OPC module 1 d adds such negative OPC patterns 161 a, 161 b, 161 c, and 161 d so as to cover the window portions 151 a, 151 b, 151 c, and 151 d, respectively.

As input device shown in FIG. 1, may be for example, a keyboard, a mouse, a recognition device such as an optical character readers (OCR), a drawing input device such an image scanner, or a special input device such a voice input device. The output device 9 can display the design data 110, the resized data 120, the first mask data 130 and 140, the second mask data 150 and 160 and the like with a monitor, and can print such data. The output device 9 may be a display device such a liquid crystal display (LCD), CRT display, or a printing device such a ink jet printer or a laser printer.

The main memory 7 has a read-only memory (ROM) and a random-access memory (RAM). The ROM serves as a program storage device for storing a program executed by the CPU 1 (the details of the program are described later.). The RAM serves as a temporary data memory for storing data used in executing a program by the CPU 1, and used as a working domain. As the main memory 7, a semiconductor memory, a magnetic disk, an optical disc, a magneto-optical disc and a magnetic tape, can be used. Specifically, a flexible disk, a CD-ROM, a MO disk, a cassette tape and an open reel tape, etc. can be used.

The mask data generation system shown in FIG. 1 further includes an input-output control unit (interface), which is omitted from illustration, connecting to the input device 8, the output device 9 with the CPU 1. The CPU 1 further includes a storage device management module, omitted from illustration. The storage device management module manages the design data storage device 2, the process condition storage device 3, the resizing quantity storage device 4, the space quantity storage device 5, and the mask data storage device 6.

Next, a description will be given of an example of a method of generating mask data according to the first embodiment of the present invention, referring to a flowchart of FIG. 7, and referring to FIGS. 2 to 6B as an example.

(a) In step S1 of FIG. 7, the design data 110 shown in FIG. 2 is prepared. The design data 110 may be stored in advance in the design data storage device 2 shown in FIG. 1. On the other hand, the design data 110 may be input using the input device 8 and stored in the design data storage device 2. In step S2, the resized data generation module 1 a shown in FIG. 1 reads a resizing quantity ΔD₁ stored in the resizing quantity storage device 4 and the design data 110 shown in FIG. 2 stored in the design data storage device 2. The resized data generation module 1 a then generates resized data 120 having resized patterns 120 a, 120 b, 120 c, and 120 d by equally enlarging each of the respective design patterns 110 a, 110 b, 110 c, and 110 d of the design data 110, as shown in FIG. 3, by the resizing quantity ΔD₁.

(b) In step S3, the first mask data generation module 1 b shown in FIG. 1 reads a space quantity ΔS stored in the space quantity storage device 5 and the resized data 120 shown in FIG. 3 generated in step S2. The first mask data generation module 1 b then determines areas having space width S_(d3), which is the space quantity ΔS or less from among areas which are sandwiched by the resized patterns 120 a, 120 b, 120 c, and 120 d of the resized data 120, as the space areas 123 a, 123 b, 123 c, and 123 d. Then, the first mask data generation module 1 b generates first mask data 130 by filling the space areas 123 a, 123 b, 123 c, and 123 d shown in FIG. 4. In step S4, the second mask data generation module 1 c shown in FIG. 1 reads the resizing quantity ΔD₁ stored in the resizing quantity storage device 4, and the resized data 120 shown in FIG. 3 and generated in step S2. Then, as shown in FIG. 5, the second mask data generation module 1 c generates second mask data 150 having four window portions 151 a, 151 b, 151 c, and 151 d for selectively exposing areas determined by enlarging the space areas 123 a, 123 b, 123 c, and 123 d of the resized data 120 shown in FIG. 3, by the resizing quantity ΔD₁.

(c) In step S5, the OPC module 1 d shown in FIG. 1 performs OPC on the first mask data 130 generated in step S3. Consequently, as shown in FIG. 6A, rectangular positive OPC patterns 143 a, 143 b, 143 c, and 143 d, and rectangular negative OPC patterns 144 a and 144 b are added. Furthermore, the OPC module 1 d shown in FIG. 1 also performs OPC on the second mask data 150, shown in FIG. 5, generated in step S4. Consequently, as shown in FIG. 6B, negative patterns 161 a, 161 b, 161 c, and 161 d are added so as to cover the window portions 151 a, 151 b, 151 c, and 151 d. The first mask data 140 and the second mask data 160 on which OPC has been performed are stored in the mask data storage device 6 shown in FIG. 1.

(e) In step S6, the first mask data 140 and the second mask data 160 on which OPC has been performed in step S5 are converted to data for a pattern generator such an electron beam (EB) writing device respectively. Then, a set of masks which includes a first mask 10 shown in FIG. 8A and a second mask 20 shown in FIG. 9A is produced using an unillustrated pattern generator based on the converted first mask data 140 and the converted second mask data 160.

According to the method of generating mask data according to the first embodiment, it is possible to produce a set of masks which can delineate circuit patterns having both a target line width, which is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system, and a target space width, which is the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system. Note that the method of generating mask data according to the first embodiment of the present invention is an example. The method is not limited to the procedures of the steps S1 to S6, and other various procedures can be adopted.

Moreover, the line width W_(d0) of the thin line patterns 110 a, 110 b, 110 c, and 110 d does not need to be smaller than the minimum line width W_(min). That is, the line width W_(d0) may be equal to, or may be larger than the minimum line width W_(min). When the line width W_(d0) is larger than the minimum line width W_(min), it is possible to obtain an increased lithography margin corresponding to a difference quantity from the minimum line width W_(min) and as the resizing quantity ΔD₁ in the thin line portions 112 a, 112 b, 112 c, and 112 d.

The space width S_(d0) of thin line patterns 110 a, 110 b, 110 c, and 110 d does not need to be equal to the minimum space width S_(min). That is, the space width S_(d0) may be larger than the minimum space width S_(min). When the space width is larger than the minimum space width S_(min), it is possible to obtain an increased lithography margin corresponding to a difference quantity of the minimum space width S_(min) in the window portions 151 a, 151 b, 151 c, and 151 d.

The procedures of Steps S1 to S6 shown in FIG. 7 can be executed by control the CPU 1 by a program (mask data generation program) which algorisms thereof equal to the procedures of Steps S1 to S6. The program includes: generating resized data by equally enlarging design patterns of design data stored in the design data storage device 2 by a resizing quantity ΔD₁ stored in the resizing quantity storage device 4, by the resized data generation module 1 a shown in FIG. 1; generating first mask data by filling the space areas of the enlarged resized data determined by filling space areas having a space which is a predetermined space quantity ΔS or less stored in the space quantity storage device 5 of the resized data, by the first mask data generation module 1 b; generating second mask data, which can be aligned with the first mask data, having window portions for selectively exposing areas determined by enlarging the space areas by the resizing quantity ΔD₁, by the second mask data generation module 1 c; performing OPC on the first and second mask data by the OPC module 1 d; and the like. The program may be stored in the main memory 7 and the like of the mask data generation system shown in FIG. 1. The program can be stored in a computer-readable storage medium. The procedures of the method of generating mask data can be performed, by reading the program from the computer-readable storage medium to the main memory 7.

Here, the “computer-readable storage medium” means any media and the like that can store a program, including, e.g., external memory units, semiconductor memories, magnetic disks, optical disks, magneto-optical disks, magnetic tape, and the like for a computer. To be more specific, the “computer-readable storage media” include flexible disks, CD-ROMs, MO disks, cassette tape, open reel tape, and the like. For example, the main body of the mask data generation system can be configured to incorporate a flexible disk drive and an optical disk drive, or to be externally connected thereto. A flexible disk is inserted into the flexible disk drive from a slot, a CD-ROM is inserted into the optical disk drive from a slot, and then a given readout operation is executed, whereby programs stored in these storage media can be installed on the main memory 7. In addition, by connecting given drives to the mask data generation system, it is also possible to use, for example, a ROM as a memory unit employed for a game pack or the like, and cassette tape as magnetic tape. Furthermore, it is possible to store a program in another program storage device via an information processing network, such as the Internet.

As shown in FIGS. 8A and 9A, the set of masks according to the first embodiment of the present invention is a set of photomasks for forming, on a target (semiconductor substrate) to be exposed, thin line portions having a line width smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system used in the photolithography processes, by slimming the line widths of patterns after exposure by a predetermined quantity. The set of masks includes the first mask 10 having thin line patterns 11 a and 11 b for forming the thin line portions, and the second mask 20 having window portions 23 a, 23 b, 23 c, and 23 d for removing unnecessary parts from the patterns formed by use of the first mask 10.

The first mask 10 shown in FIGS. 8A and 8B includes a first mask plate 10 a and a first mask pattern 11 placed on the first mask plate 10 a. As shown in FIG. 8A, the first mask pattern 11 includes the two stripe-shaped thin line patterns 11 a and 11 b, and a pair of connection patterns 12 a and 12 b which sandwich the two thin line patterns 11 a and 11 b at both ends thereof and connect the thin line patterns 11 a and 11 b with each other. The thin line patterns 11 a and 11 b are separated from each other by a space width S_(m1) therebetween in the Y-axis direction and arranged with a line width W_(m1) in the X-axis direction. The first mask plate 10 a is exposed at a window portion 15, the interior surrounded by the two thin line patterns 11 a and 11 b and the pair of connection patterns 12 a and 12 b.

Rectangular positive OPC patterns 13 a, 13 b, 13 c, and 13 d are respectively added to four outer corners of the pair of connection patterns 12 a and 12 b. Partial areas of the positive OPC patterns 13 a, 13 b, 13 c, and 13 d are superimposed on the respective corners of the connection patterns 12 a and 12 b. The areas of the positive OPC patterns 13 a, 13 b, 13 c, and 13 d which are not superimposed on the connection patterns 12 a and 12 b protrude, each in an L-shape, from the respective four outer corners of the connection patterns 12 a and 12 b. In addition, rectangular negative OPC patterns 14 a and 14 b are respectively added to both sides of the window portion 15 in the X-axis direction. The positive OPC patterns 13 a, 13 b, 13 c, and 13 d and the negative OPC patterns 14 a and 14 b are patterns which have been added through OPC for controlling optical proximity effects during exposure. The negative OPC patterns 14 a and 14 b are partially superimposed on parts of the thin line patterns 11 a and 11 b and parts of the connections patterns 12 a and 12 b. Of the entire areas of the thin line patterns 11 a and 11 b and the connection patterns 12 a and 12 b, areas on which the negative OPC patterns 14 a and 14 b are superimposed are each cut out in a C-shape. The first mask plate 10 a is exposed at the C-shaped cut-out areas and the interior of the window portion 15.

On the other hand, the second mask 20 shown in FIGS. 9A and 9B includes a second mask plate 20 a and a second mask pattern 21 placed on the second mask plate 20 a. As shown in FIG. 9A, the second mask pattern 21 has four rectangular window portions 22 a, 22 b, 22 c, and 22 d. The two window portions 22 a and 22 b have the same shapes and are separated from each other along a single line in the X-axis direction. The length of sides along the Y-axis direction of the window portions 22 a and 22 b is equal to a space width S_(m2). The two window portions 22 c and 22 d have the same shape. The two window portions 22 c and 22 d are separated from each other along a single line in the Y-axis direction and provided line-symmetrically relative to a line connecting the two window portions 22 a and 22 b. The length of sides along the X-axis direction of the two window portions 22 c and 22 d is also equal to the space width S_(m2).

In the second mask pattern 21, four rectangular negative OPC patterns 23 a, 23 b, 23 c, and 23 d are provided which are superimposed on the four window portions 22 a, 22 b, 22 c, and 22 d so as to cover the window portions 22 a, 22 b, 22 c, and 22 d, respectively. Each of the negative OPC patterns 23 a and 23 b has a side that is longer than the space width S_(m2) in the Y-axis direction. Each of the negative OPC patterns 23 c and 23 d has a side that is longer than the space width S_(m2) in the X-axis direction. The second mask plate 20 a is exposed at the interiors of the negative OPC patterns 23 a, 23 b, 23 c, and 23 d. That is, the negative OPC patterns 23 a, 23 b, 23 c, and 23 d serve as transmission patterns.

The first mask pattern 11 shown in FIG. 8A and the second mask pattern 21 shown in FIG. 9A can be aligned with each other as shown in FIG. 10. The window portions 22 a and 22 b of the second mask pattern 21 are aligned, on the basis of the space width S_(m2) in the Y-axis direction, with the center portions of the connection patterns 12 a and 12 b of the first mask pattern 11, respectively. That is, the window portions 22 a and 22 b are each patterns for dividing a pattern to be provided on the semiconductor substrate from the connection pattern 12 a or 12 b in the photolithography processes into two patterns in the Y-axis direction. The window portions 22 c and 22 d are aligned, on the basis of the space width S_(m2) in the X-axis direction, with center portions of the thin line patterns 11 a and 11 b of the first mask pattern 11, respectively. That is, the two window portions 22 c and 22 d are each patterns for dividing a strip to be provided on the semiconductor substrate from the thin line portion 11 a or 11 b in the photolithography processes, into two patterns in the X-axis direction. Note that the first and second mask patterns 11 and 21 are enlarged to five (or four) times the pattern dimensions to be projected, because the reduction ratio of the optical system of a projection exposure system is 1/5 (or 1/4).

As the material for the first mask plate 10 a shown in FIG. 8B and of the second mask plate 20 a shown in FIG. 9B, it is possible to use quartz glass, soda-lime glass, borosilicate glass, or the like. Moreover, as the material for the first and second mask patterns 11 and 21, it is possible to use chromium (Cr), a composite film of Cr and a chromium oxide (Cr₂O₃), or the like. Alternatively, it may be possible to adopt a translucent film employed for an attenuated phase shift mask (half tone phase shift mask), often used in a today's technology, in which a film is configured such that a mask pattern portion is translucent to exposure light and the phase of light in this portion is shifted by 180 degrees from the phase of light passing through the mask plate. For the translucent film employed for the half tone phase shift mask, it is possible to use a molybdenum silicide oxynitride (MoSiO_(x)N_(y)), a chromium oxide (Cr_(x)O_(y)), or the like.

According to the set of masks of the first embodiment, it is possible to delineate a circuit pattern including both a target line width that is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system, and a target space width that equal to the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system.

Next, a description will be given of a method for forming a pattern according to the first embodiment of the present invention with reference to FIGS. 11 to 19B.

(a) First, an n⁺ single crystal silicon wafer is prepared. Subsequently, a device area (active area) is deposited on a surface of the n+ single crystal silicon wafer. The circumference of the device area is defined by an unillustrated field oxide layer. An unillustrated plurality of n-type and p-type semiconductor areas are formed in the device area by ion implantation or the like. As a result, a semiconductor substrate 31 shown in FIG. 11 is prepared.

(b) Next, a gate oxide film (first insulator) 31 a with a thickness of about 3 to 300 nm is deposited on the semiconductor substrate 31. If the gate oxide is a tunnel gate oxide, the thickness of the first insulator may be about 1.5 nm. Thereafter, a process-target film 32 made of polycrystalline silicon or the like is deposited on the first insulator 31 a by chemical vapor deposition (CVD) or the like. Subsequently, an underlying mask film (second insulator) 33 is deposited on the process-target film 32 by CVD or the like. Note that if the underlying mask film 33 is a silicon nitride Si_(x)N_(y)) film, a silicon oxynitride (SiO_(x)N_(y)) film, or the like when the process-target film 32 is made of polycrystalline silicon, etching selectivity can be ensured. The underlying mask film 33 does not need to be an insulator as long as it is a film which can ensure a sufficiently high etching rate compared with the etching rate of the process-target film 32. It is preferable that the thickness of the underlying mask film 33 be about 50 to 100 nm.

(c) Next, a first resist film 34 is spin-coated on the underlying mask film 33. Subsequently, the first mask 10 shown in FIG. 8A is mounted on an unillustrated projection exposure system, and then the pattern of the first mask 10 is reduced to, e.g., 1/5 (or 1/4) and transferred onto the first resist film 34. Thereafter, the first resist film 34 is developed, and thus a first resist pattern 34 a is delineated as shown in FIGS. 12A and 12B. The first resist pattern 34 a includes two thin line portions 34 p and 34 q and a pair of connection portions 34 k and 34 l which sandwich the two thin line portions 34 p and 34 q at both ends thereof and connect the thin line portions 34 p and 34 q with each other. The two thin line portions 34 p and 34 q are separated from each other by a space width S_(p1) therebetween in the Y-axis direction and arranged in parallel to each other by a line width W_(p1) in the X-axis direction. Part of the base mask 33 is exposed at a window portion 37. The interior of the window portion 37 is surrounded by the two thin line portions 34 p and 34 q and the pair of connection portions 34 k and 34 l.

(d) Next, the first resist pattern 34 a is slimmed by a resizing quantity ΔL₁ (=ΔD₁) by plasma ashing using oxygen (O) or the like, whereby a resized resist pattern 34 b is delineated as shown in FIGS. 13A and 13B. In other words, thin line portions 34 r and 34 s with a target line width W_(p2) are formed by slimming the thin line portions 34 p and 34 q with the line width W_(p1) which is determined by the first resist pattern 34 a. The target line width W_(p2) may be smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system. The resized resist pattern 34 b includes the two thin line portions 34 r and 34 s and a pair of connection portions 34 m and 34 n which sandwich the two thin line portions 34 r and 34 s at both sides thereof and connect the thin line portions 34 r and 34 s with each other. The two thin line portions 34 r and 34 s are separated from each other by a space width S_(p2) therebetween and arranged in parallel to each other by the target line width W_(p2) in the X-axis direction. The underlying mask film 33 is exposed at a window portion 37 a. The interior of the window portion 37 a is surrounded by the two thin line portions 34 r and 34 s and the pair of connection portions 34 m and 34 n. With the resized resist pattern 34 b as an etching mask, part of the base mask 33 is selectively removed by reactive ion etching (RIE) or the like.

As a result, thin line portions 33 r and 33 s and connection portions (not shown) of an underlying mask pattern (insulator pattern) 33 a as shown in FIG. 14 are delineated. The resized resist pattern 34 b is removed by use of a resist remover or the like.

(e) Next, as shown in FIG. 15, a second resist film 35 is spin-coated on the process-target film 32 and the underlying mask pattern 33 a. Subsequently, the second mask 20 shown in FIG. 9A is mounted on the unillustrated projection exposure system, and then the pattern of the second mask 20 is reduced to, e.g., 1/5 (or 1/4) and transferred onto the second resist film 35. Thereafter, the second resist film 35 is developed, and thus a second resist pattern 35 a as shown in FIGS. 16A and 16B is delineated. The second resist pattern 35 a has four rectangular window portions 36 a, 36 b, 36 c, and 36 d. The two window portions 36 a and 36 b have the same shapes and are separated from each other along a single line in the X-axis direction. The two window portions 36 a and 36 b expose parts of the connection portions 33 n and 33 m of the underlying mask pattern 33 a, respectively, each by a length of a target space width S_(p3) in the Y-axis direction. The target space width S_(p3) may be the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system. The two window portions 36 c and 36 d, having the same shapes, are separated from each other along a single line in the Y-axis direction and provided line-symmetrically relative to a line connecting the two window portions 36 a and 36 b. The two window portions 36 c and 36 d expose parts of the thin line portions 33 r and 33 s of the underlying mask pattern 33 a, respectively, each by a length of the target space width S_(p3), in the X-axis direction. Further, part of the process-target film 32 is exposed at the interiors of the window portions 36 a, 36 b, 36 c, and 36 d.

(f) Next, with the second resist pattern 35 a as a mask, parts of the thin line portions 33 r and 33 s and connection portions 33 m and 33 n of the underlying mask pattern 33 a are selectively removed by RIE or the like, thus dividing each portion into two portions. As a result, an underlying mask pattern (insulator pattern) 33 b is delineated as shown in FIG. 17. The second resist pattern 35 a is removed by use of a resist remover or the like. Thereafter, with the underlying mask pattern 33 b as a mask, part of the process-target film 32 is selectively removed by RIE or the like. Consequently, four process-target film patterns (circuit patterns) 32 a, 32 b, 32 c, and 32 d as shown in FIG. 18 (where 32 c, and 32 d are not shown) are delineated. Thereafter, the remaining underlying mask pattern 33 b is removed by use of hydrofluoric acid (HF) or the like. As shown in FIGS. 19A and 19B, the four process-target film patterns 32 a, 32 b, 32 c, and 32 d have the same shapes and positional relationships of line-symmetry (mirror symmetry) with one another. The four process-target film patterns 32 a, 32 b, 32 c, and 32 d include four stripe-shaped thin line portions 39 a, 39 b, 39 c, and 39 d, respectively, and rectangular portions 38 a, 38 b, 38 c, and 38 d, respectively, each of which has a substantially square shape and is connected with an outer end portion in the X-axis direction of the corresponding thin line portion 39 a, 39 b, 39 c, or 39 d. The two thin line portions 39 a and 39 c are separated from each other by the target space width S_(p3) therebetween and arranged by the target line width W_(p2) along a single line. The two thin line portions 39 b and 39 d are also separated from each other by the target space width S_(p3) therebetween and arranged by the target line width W_(p2) along a single line. The two thin line portions 39 a and 39 b are separated from each other in parallel, by the space width S_(p2) therebetween in the Y-axis direction. Similarly, the two thin line portions 39 c and 39 d are separated from each other in parallel, by the space width S_(p2) therebetween in the Y-axis direction. The rectangular portions 38 a and 38 b are separated by the target space width S_(ps) therebetween in the Y-axis direction. The rectangular portions 38 c, and 38 d are separated by the target space width S_(p3) therebetween in the Y-axis direction.

According to the first embodiment, it is possible to delineated the process-target film patterns (circuit patterns) 32 a to 32 d having both the target line width W_(p2), which is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system, and the target space width S_(p3), which is the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system. It should be noted that the method for forming a pattern according to this embodiment is an example. The method is not limited to the procedure shown in FIGS. 11 to 19B, and other various procedures can be adopted.

Moreover, the target line width W_(p2) does not need to be smaller than the minimum line width W_(min). That is, the target line width W_(p2) may be equal to, or may be larger than, the minimum line width W_(min). When the target line width W_(p2) is larger than the minimum line width W_(min), it is possible to obtain an increased lithography margin corresponding to a difference quantity from the minimum line width W_(min) and the resizing quantity ΔL₁, for the line width of the first resist pattern.

Furthermore, the target space width S_(p3) does not need to equal to the minimum space width S_(min). That is, the target space width S_(p3) may be larger than the minimum space width S_(min). When the space width is larger than the minimum space width S_(min), it is possible to obtain an increased lithography margin corresponding to a difference quantity from the minimum space width S_(min) in the second resist pattern.

[First Modification]

In a method for forming a pattern according to a first modification of the first embodiment of the present invention, instead of the procedures shown in FIGS. 13A to 14, the following procedure is performed. As shown in FIG. 20, the first resist pattern 34 a shown in FIGS. 12A and 12B is slimmed by etching such as RIE for a longer etching time than the just-etching time by the resizing quantity ΔL₁ (=ΔD₁), and at the same time, part of the underlying mask film 33 is selectively removed so that the residual part thereof has the line width W_(p2) that is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system. That is, the thin line portions 33 r and 33 s of the underlying mask pattern (insulator pattern) 33 a, which has the same shape as that of the resized resist pattern 34 b obtained by slimming the first resist pattern 34 a, are delineated by over etching.

Note that the resized resist pattern 34 b and the underlying mask pattern 33 a do not need to be completely identical in shape. Such etching is allowable as to create an under-cut portion where the underlying mask pattern 33 a is thinner. In any case, in order to slim the underlying mask pattern 33 a by over etching, an etching gas for use in RIE is selected so that the etching rate of the underlying mask film 33 is 10 to 1000 times, preferably 30 to 1000 times, more preferably 100 to 1000 times as high as the etching rate of the process-target film 32. Other procedures, which are similar to the procedures shown in FIGS. 11, 15 to 19B, are omitted.

According to the first modification of the first embodiment of the present invention, the same as in the first embodiment, it is also possible to delineate the process-target film patterns (circuit patterns) 32 a to 32 d having both the target line width W_(p2), which is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system, and the target space width S_(p3), which is the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system, when the procedures shown in FIGS. 20A and 20B are adopted instead of the procedures shown in FIGS. 12A to 14.

[Second Modification]

In a method for forming a pattern according to a second modification of the first embodiment of the present invention, instead of the procedures shown in FIGS. 13A to 14, the following procedures are performed. With the first resist pattern 34 a shown in FIG. 12A as an etching mask, part of the underlying mask film 33 is selectively removed by RIE or the like. As a result, the underlying mask pattern (insulator pattern) 33 a is delineated as shown in FIG. 21. The first resist pattern 34 a is removed by use of a resist remover or the like. Thereafter, as shown in FIG. 22, the underlying mask film 33 is slightly etched by use of, when the underlying mask film 33 is an oxide film, an oxide etchant such as HF to slim the underlying mask pattern 33 a by ΔL₁ (=ΔD₁), thus delineating the thin line portions 33 r and 33 s of the underlying mask pattern 33 a. Needless to say, in terms of controllability, it is preferable to slightly etch the underlying mask film 33, not by wet etching but by dry etching. Other procedures, which are the same as the procedures shown in FIGS. 11 to 12B, and 15 to 19B, are omitted.

According to the second modification of the first embodiment of the present invention, the same as the first embodiment, it is possible to obtain the process-target film patterns (circuit patterns) 32 a to 32 d, having both the target line width W_(p2), which is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system, and the target space width S_(p3), which is system the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system, when the procedures shown in FIGS. 21 and 22 are adopted instead of the procedures shown in FIGS. 13A to 14.

(Second Embodiment)

As shown in FIG. 23, a mask data generation system according to the second embodiment of the present invention includes a central processing unit (CPU) 11 x, a design data storage device 2, a process condition storage device 3, a resizing quantity storage device 4, a space quantity storage device 5, a mask data storage device 6, a main memory 7, an input device 8, and an output device 9.

The design data storage device 2 stores design data 210 shown in FIG. 24 instead of the design data 110 shown in FIG. 2. The design data 210 includes four design patterns 110 a, 110 b, 110 c, and 110 d for forming desired process-target film patterns on a semiconductor substrate, the same as design data 110. The design patterns 110 a, 110 b, 110 c, and 110 d all have a line symmetrical (mirror symmetrical) relationship and have the same shape with one another. The two thin line portion 112 a and 112 b are separated from each other by the space width S_(d0) therebetween in the X-axis direction. The two thin line portion 112 c and 112 d are also separated from each other by the space width S_(d0) therebetween in the X-axis direction. The two rectangular portions 111 a and 111 c are also separated from each other by the space width S_(d6) therebetween in the Y-axis direction. The two rectangular portions 111 b and 111 d are also separated from each other by the space width S_(d6) therebetween in the Y-axis direction.

Here, the space width S_(d6) is different from the space width Sd₀ shown in FIG. 2 in that the space width S_(d6) may be smaller than the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system. The space width S_(d6) is determined based on a space width reducing quantity ΔD₂ by a process such an on overcoat method or a thermal flow process (TF process) for reducing the space width after exposure processes. The two thin line portions 112 a and 112 c are separated from each other by the space width S_(d5) therebetween in the Y-axis direction. The two thin line portions 112 d and 112 b are also separated from each other by the space width S_(d5) therebetween in the Y-axis direction.

The process condition storage device 3 shown in FIG. 23 further stores a space width reducing quantity ΔD₂ by process for reducing the space width after exposure processes. The process condition storage device 3 further stores a process proximity effect quantity such as a change quantity of the space width reducing quantity ΔD₂ generated by conditions of surrounding patterns in processes for slimming the space width after exposure processes.

The CPU 1 x is different from the CPU 1 shown in FIG. 1 in that the CPU 1 x further includes a space area correction module 1 e and a process proximity correction module if in addition to the resized data generation module 1 a, the first mask data generation module 1 b, the second mask data generation module 1 c, and the OPC module 1 d.

The resized data generation module 1 a generates, for example, as shown in FIG. 25, resized data 220 having resized patterns 120 a, 120 b, 120 c, and 120 d by equally enlarging the design patterns 110 a, 110 b, 110 c, and 110 d shown in FIG. 24 by the resizing quantity ΔD₁. The space width S_(d8), from which each of the two thin line portions 122 a and 122 b, the two thin line portions 122 c and 122 d, the two rectangular portions 121 a and 121 c, and the two rectangular portions 121 b and 121 d are respectively separated, is smaller than the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system. Moreover, each of the two thin line portions 122 a and 122 c, and the two thin line portions 122 b and 122 d are separated from each other by the space width S_(d7) in the Y-axis direction.

As shown in FIG. 26, the first mask data generation module 1 b shown in FIG. 23, for example, generates first mask data 230 by filling the space areas 123 a, 123 b, 123 c, and 123 d, having a space width S_(d8) which is the space quantity ΔS or less, in the resized data 120 shown in FIG. 25. The first mask data 230 includes two thin line patterns 231 a and 231 b, and a pair of thin line patterns 232 a and 232 b which connect with each other and which sandwich both ends of the two thin line patterns 131 a and 131 b.

As shown in FIG. 27, the second mask data generation module 1 c shown in FIG. 23 generates second mask data 250 having four window portions 251 a, 251 b, 251 c, and 251 d by enlarging the space areas 123 a, 123 b, 123 c, and 123 d of the resized data 120 shown in FIG. 25 by the resizing quantity ΔD₁. The second mask data 250 is a data of patterns, which can be aligned with the first mask data 230. The four window portions 251 a, 251 b, 251 c, and 251 d are patterns for exposing portions of the thin line patterns 232 a, 232 b, 231 a and 231 b shown in FIG. 25 having the space width S_(d6), at the positions of the space areas 123 a, 123 b, 123 c, 124 d.

The space area correction module 1 e shown in FIG. 23 reads process conditions stored in the process condition storage device 3 and estimates the space width reducing quantity ΔD₂ for reducing a space width of patterns corresponding to the window portions 251 a, 251 b, 251 c, and 251 d on a semiconductor substrate after exposure processes. The space area correction module 1 e then reads the second mask data generated by the second mask data generation module 1 c and enlarges the respective window portions of the second mask data by the estimated space width reducing quantity ΔD₂. Note that the space area correction module 1 e may reads the space width reducing quantity ΔD₂ which is predetermined stored in the process condition storage device 3.

For example, the space area correction module 1 e enlarges the window portions 251 a, 251 b, 251 c, and 251 d of the second mask data 250 shown in FIG. 27 by the space width reducing quantity ΔD₂. Consequently, as shown in FIG. 29A, the second mask data 260, which includes window portions 261 a and 261 b having a side by the space width S_(d9) in Y-axis direction and window portions 261 c and 261 d having by the space width S_(d9) in the X-axis direction, is generated. Here, the space width S_(d9) is a dimension with which a pattern can be optically resolved by a projection exposure system. That is, the space width S_(d6) of the design data 210 is determined so as to be larger than a half value of a dimension subtracted the space width reducing quantity ΔD₂ from the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system.

For example, the OPC module 1 d shown in FIG. 23 performs OPC on the first mask data 230 shown in FIG. 26. Consequently, as shown in FIG. 29A, rectangular positive OPC patterns 243 a to 243 d and rectangular negative patterns 244 a and 244 b are added. The positive OPC patterns 243 a to 243 d are partially superimposed on four corners of the thin line patterns 232 a and 232 b. Moreover, the negative patterns 244 a and 244 b are partially superimposed on the two thin line patterns 231 a and 231 b and the thin line patterns 232 a and 232 b in a C-shape, in vicinities of both ends of the window portions 233 in the X-axis direction.

Furthermore, the OPC module 11 d shown in FIG. 23 performs OPC on the second mask data having the window portions enlarged by the space area correction module 1 e. For example, as shown in FIG. 29B, the OPC module 11 d adds negative patterns 271 a and 271 b so as to cover the window portions 261 a and 261 b and negative patterns 271 c and 271 d so as to cover the window portions 261 c and 261 d, by performing OPC on the second mask data 260 shown in FIG. 28.

The process proximity correction module 1 f shown in FIG. 23 reads a process proximity correction quantity stored in the process condition storage device 3, and estimates process proximity effects when patterns are delineated. The process proximity correction module if then performs process proximity correction on the first mask data 240 and the second mask data 270 respectively. It is possible to prevent process proximity effects in processes for slimming the space width.

Next, a description will be given of an example of a method of generating mask data according to the second embodiment of the present invention, referring to a flowchart of FIG. 30.

(a) In step S1 of FIG. 30, as shown in FIG. 24, design data 210 is prepared. The design data 210 includes, the same as the design data 110, four design patterns 110 a, 110 b, 110 c, and 110 d for forming desired process-target film patterns on a semiconductor substrate, and have a line symmetrical (mirror symmetrical) relationship with one another. In step S2, as shown in FIG. 25, the resized data generation module 1 a shown in FIG. 23 generates resized data 220 having resized patterns 120 a, 120 b, 120 c, and 120 d by equally enlarging the design patterns 110 a, 110 b, 110 c, and 110 d shown in FIG. 24 by the resizing quantity ΔD₁.

(b) In step S3, the first mask data generation module 1 b shown in FIG. 23 generates first mask data 230 shown in FIG. 26 by filling the space areas 123 a, 123 b, 123 c, and 123 d having the space width S_(d8), which is the space quantity ΔS or less, sandwiched at two sides of the thin line portions 122 a, 122 b, 122 c, and 122 d in the resized data 120 shown in FIG. 25. In step S4, as shown in FIG. 27, the second mask data generation module 1 c shown in FIG. 23 generates second mask data 250 having four window portions 251 a, 251 b, 251 c, and 251 d by enlarging the space areas 123 a, 123 b, 123 c, and 123 d of the resized data 220 shown in FIG. 25 by the resizing quantity ΔD₁. The window portions 251 a, 251 b, 251 c, and 251 d expose parts of the thin line patterns 231 a, 231 b, 232 a and 232 b having the space width S_(d6), at the positions of the space areas 123 a, 123 b, 123 c, and 123 d.

(c) In step S4 x, the space area correction module 1 e shown in FIG. 23 reads the second mask data 250 generated in step S4, and a space width reducing quantity ΔD₂ stored in the process condition storage device 3. The space area correction module 1 e then generates second mask data 260 by enlarging the window portions 251 a, 251 b, 251 c, and 251 d of the second mask data 250 by the space width reducing quantity ΔD₂ as shown in FIG. 28. The second mask data 260 includes the window portions 261 a and 261 b having one side by the space width S_(d9) in the Y-axis direction and the window portions 261 c and 261 d having one side by the space width S_(d9) in the X-axis direction.

(d) In step S5, the OPC module 14 d shown in FIG. 23 performs OPC on the first mask data 230 shown in FIG. 26. Consequently, as shown in FIG. 29A, rectangular positive OPC patterns 243 a to 243 d and rectangular negative patterns 244 a and 244 b are added. Furthermore, the OPC module 14 d shown in FIG. 23 performs OPC on the second mask data 260 shown in FIG. 28. Consequently, as shown in FIG. 29B, negative OPC patterns 271 a, 271 b, 271 c, and 271 d, which cover the window portions 261 a, 261 b, 261 c, and 261 d, are added.

(e) In step S5 x, the process proximity correction module if shown in FIG. 23 reads process condition stored in the process condition storage device 3, and estimates process proximity effects in process for reducing the space width when patterns are formed. The process proximity correction module if then performs process proximity correction on each of the first mask data 240 and the second mask data 270. The first mask data 240 and the second mask data 270 on which process proximity corrections have been performed are stored in the mask data storage device 6.

(f) In step S6, the first mask data 240 and the second mask data 27 are converted to data for a pattern generator such an EB writing device respectively. Then, a first mask 40 shown in FIG. 31 and a second mask 50 shown in FIG. 32 are produced with the pattern generator, based on the converted first mask data 240 and the converted second mask data 270.

According to a method of generating mask data according to the second embodiment of the present invention, it is possible to provide a set of mask which can delineate circuit patterns having both a target line width, which is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system, and the target space width, which is the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system. Note that, the method of generating mask data according to the second embodiment the present invention is an example, ant the method is not limited to step S1 to S6, and the method can be used with other various process.

Moreover, the line width W_(d0) of the design data 210 does not need to be smaller than the minimum line width W_(min). That is, the line width W_(d0) may be equal to, or may be larger than, the minimum line width W_(min). When the line width W_(d0) is larger than the minimum line width W_(min), it is possible to obtain an increased lithography margin corresponding to a difference quantity from the minimum line width W_(min) and the resizing quantity ΔD₁.

Furthermore, the space width S_(d6) does not need to be smaller than the minimum space width S_(min). That is, the space width S_(d6) may be equal to, or may be larger than, the minimum space width S_(min). When the space width S_(d6) is larger than the minimum space width S_(min), it is possible to obtain an increased lithography margin corresponding to a difference quantity from the minimum space width S_(min), and the space width reducing quantity ΔD₂.

As shown in FIGS. 31 and 32, the set of masks according to the second embodiment of the present invention is a set of photomasks for forming, on a semiconductor substrate, thin line portions having a line width smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system, by slimming the line width of patterns after exposure by a predetermined quantity. The set of masks includes a first mask 40 having thin line patterns 41 a and 41 b for forming the thin line portion, and a second mask 50 having the window portions 52 a, 52 b, 52 c, and 52 d for removing unnecessary parts from the patterns formed by use of the first mask 40.

As shown in FIG. 31, the first mask 40 includes a first mask plate 40 a, and a first mask pattern 41 placed on the first mask plate 40 a. The first mask pattern 41 includes the two stripe-shaped thin line patterns 41 a and 41 b, and a pair of connection patterns 42 a and 42 b which sandwich a both ends of the two thin line pattern 41 a and 41 b and are connected with each other. The two thin line pattern 41 a, 41 b are separated from each other in parallel by the line width W_(m1) therebetween in the X-axis direction.

A window portion 45 surrounded by the two thin line pattern 41 a and 41 b and the pair of the connection patterns 42 a and 42 b exposes the first mask plate 40 a. Rectangular positive OPC patterns 43 a to 43 d are placed respectively at four outer corners of the pair of the connection patterns 42 a and 42 b. Rectangular negative patterns 44 a and 44 b are placed at both ends of the window portions 45 in the X-axis direction. The positive OPC patterns 43 a to 43 d, and the negative OPC patterns 44 a and 44 b are added for preventing optical proximity effects in the exposing process.

The second mask 50 shown in FIG. 32 includes a second mask plate 50 a and a second mask pattern 51 placed on the second mask plate 50 a. The second mask pattern 51 includes the four rectangular window portions 52 a, 52 b, 52 c, and 52 d. The window portions 52 a and 52 b are separated from each other along a single line in the Y-axis direction. The two window portions 52 c and 52 d are separated from each other along a single line in the X-axis direction, and have line symmetrically relative to a line connecting the two window portions 52 a and 52 b. Here, the two window portions 52 a and 52 b are separated from each other by the space width S_(m2) therebetween in the X-axis direction. The two window portions 52 c and 52 d are separated from each other by the space width S_(m2) therebetween in the Y-axis direction. In the second mask pattern 51, four rectangular negative patterns 53 a to 53 d are further placed. The negative patterns 53 a and 53 b have respective one side in Y-axis direction, which is longer than the space width S_(m5), so as to cover the two window portions 52 a and 52 b respectively. The negative patterns 53 c and 53 d have a respective one side in the X-axis direction which is longer than the space width S_(m2) so as to cover the two window portions 52 c and 52 d.

As shown in FIG. 33, the first mask pattern 41 shown in FIG. 31 and the second mask pattern 51 shown in FIG. 32 can be aligned each other. The window portions 52 a and 52 b can be aligned with the center of the respective connection patterns 42 a and 42 b with the space width S_(m2) in the Y-axis direction. That is, the window portions 52 a and 52 b are patterns for dividing the connection patterns 42 a and 42 b by the target space width. Furthermore, the window portions 52 c, 52 d can be aligned with the center of the respective thin line patterns 41 a and 41 b by the space width S_(m2) in the X-axis direction. That is, the window portions 52 c and 52 d are patterns for dividing strips on a semiconductor substrate with the target space width. Since other parts of the first mask 40 and the second mask 50 are substantially the same as the first mask 10 and the second mask 20 shown in FIGS. 8A to 10, repeated description is omitted.

According to set of masks of the second embodiment of the present invention, circuit patterns having both a target line width which is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system, and the target space width which is smaller than the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system.

Next, a description will be given of an example of a method for forming a pattern according to the second embodiment of the present invention, referring to FIG. 11, and FIGS. 34A to 43B.

(a) First, as shown in FIG. 11, a gate oxide film (first insulator) 31 a, a process-target film 32 made of polycrystalline silicon or the like, and an underlying mask film (the second insulator) 33 made of silicon nitride (Si_(x)N_(y)) or the like are deposited on the semiconductor substrate 31 respectively by CVD or the like. Then, a first resist film 34 is spin-coated on the second insulator 33. Thereafter, the first mask 40 shown in FIG. 31 is mounted on an unillustrated projection exposure system, and then the pattern of the first mask 40 is reduced, and transferred onto the first resist film 34. Then, the first resist film 34 is developed. Thus, a first resist pattern 34 c is delineated as shown in FIGS. 34A and 34B. The first resist pattern 34 c includes two thin line portions 34 t and 34 u and a pair of connection portions 34 i and 34 j which sandwich the two thin line portions 34 t and 34 u at both ends thereof and connect the two thin line portions 34 t and 34 u with each other. The two thin line portions 34 t and 34 u are separated from each other by the space width S_(p4) therebetween in the Y-axis direction and arranged in parallel by the line width W_(p1) therebetween in the X-axis direction. The interior of the window portions 37 b surrounded by the two thin line portion 34 t and 34 u and the pair of connection portions 34 i and 34 j exposes the underlying mask film 33.

(b) Next, as shown in FIGS. 35A and 35B, the first resist pattern 34 c is slimmed by the resizing quantity ΔL₁(=ΔD₁), by over etching such as by RIE for a time which is longer than a just-etching time. At the same time, parts of the underlying mask film 33 are selectively removed so as to be have the line width W_(p2) which is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system. That is, thin line portions 33 v and 33 w of the underlying mask pattern (isolation patterns) 33 c, which first resist pattern 34 c is slimmed, having the same shapes with the resized resist pattern 34 d are delineated by the over etching. The resized resist pattern 34 d includes the two thin line portions 34 v and 34 w, and the pair of connection portions 34 g and 34 h which sandwich the two thin line portions 34 v and 34 w at both ends thereof. The two thin line portions 34 v and 34 w are separated from each other by the space width S_(p5) therebetween in the Y-axis direction and arranged in parallel by the line width W_(p2) which is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system in the X-axis direction. The interior of the window portion 37 c surrounded by the two thin line portions 34 v and 34 w and the pair of the connection portions 34 g and 34 h exposes the underlying mask film 33. The resized resist pattern 34 d is removed, using a resist remover.

(c) Next, as shown in FIG. 36, second resist film 35 is spin-coated on the underlying mask pattern 33 c, and the exposed process-target film 32. Thereafter, the second mask 50 shown in FIG. 32 is mounted on an unillustrated projection exposure system, and the pattern of the second mask 50 is reduced, and transferred onto the second resist film 35. Then, as shown in FIGS. 37A and 37B, a second resist pattern 35 b having four rectangular window portions 36 e, 36 f, 36 g, and 36 h is delineated by developing the second resist film 35. The two rectangular window portions 36 e and 36 f are separated from each other along a single line in the X-axis direction. The two window portions 36 e and 36 f have the same shapes as each other, and expose connection portions 33 g and 33 h having the length of the space width S_(p3) of connection portions 33 g and 33 h of the underlying mask pattern 33 c. The two rectangular window portions 36 g and 36 h are separated from each other along a single line in the Y-axis direction are line symmetrical relative to a line connecting the two window portions 36 e and 36 f. The two window portions 36 g and 36 h are also have the same shapes as one another, and expose parts having the space width S_(p3) of the thin line portions 33 v and 33 w of the underlying mask patterns 33 a respectively.

(d) Next, an overcoat method is performed to the second resist pattern 35 b. First, as shown in FIG. 38, an over-coat film 62 made of water-soluble polymer or the like is deposited on the second resist pattern 35 b and the exposed part of the underlying mask pattern 33 c. Subsequently, this resultant is subjected to heat treatment (baking) at a temperature lower than that a temperature creating plastic deformation of the second resist pattern 35 b. Consequently, as shown in FIG. 39, the water-soluble polymer is changed to be insoluble due to the polymer's crosslinking reaction with the acid diffused from the second resist pattern 35 b, thus forming a mixed layer 62 a where part of the second resist pattern 35 b and part of the over-coat film 62 are mixed. A residual over-coat film 62 b other than the mixed layer 62 a is removed by use of a solvent such as water. As a result, the mixed layer 62 a having rectangular window portions 63 a, 63 b, 63 c, and 63 d that are narrower than the window portions 36 e, 36 f, 36 g, and 36 h, respectively, by ΔL₂ (=ΔD₁), is delineated as shown in FIGS. 40A and 40B. The underlying mask pattern 33 c is exposed in the interiors of the window portions 63 a, 63 b, 63 c, and 63 d. The window portions 63 a and 63 b expose parts of the connection portions 33 g and 33 h of the underlying mask pattern 33 c, respectively, each by a length of a target space width S_(p6) that is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system. The window portions 63 c, and 63 d also expose parts of the thin line portions 33 v and 33 w of the underlying mask pattern 33 c, respectively, each by a length of the space width S_(p6). Next, with the mixed layer 62 a and second resist pattern 35 b as an etching mask, part of the underlying mask pattern 33 c is selectively removed by RIE or the like, thereby dividing each of the thin line portions 33 v and 33 w and connection portions 33 g and 33 h of the underlying mask pattern 33 c into two portions. As a result, an underlying mask pattern (insulator pattern) 33 d as shown in FIG. 41 is delineated. The mixed layer 62 a and the second resist pattern 35 b are removed by use of a resist remover or the like.

(e) Next, as shown in FIG. 42, part of process-target film 32 is selectively removed using the underlying mask pattern 33 d as an etching mask, by such means as RIE, and thus four process-target film patterns 32 a to 32 d (the process-target film patterns 32 c, 32 d are illustrated in FIGS. 43A and 43B) are delineated. The underlying mask pattern 33 d is removed using a removent such as HF. As shown in FIGS. 43A and 43B, the process-target film patterns 32 a, 32 b, 32 c, and 32 d include thin line portions 39 a, 39 b, 39 c, and 39 d extending with the line width W_(p2) which are separated from each other by the target space width S_(p6), and the rectangular portions 38 a, 38 b, 38 c, and 38 d connected to the ends of the thin line portions 39 a, 39 b, 39 c, and 39 d respectively.

According to the second embodiment of the present invention, it is possible to delineate the process-target film patterns 32 a, 32 b, 32 c, and 32 d having both the target line width W_(p2) which is smaller than the minimum line width with which a pattern can be optically resolved by a projection exposure system, and the space width S_(p6) which is smaller than the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system.

Note that, the target line width W_(p2) does not need to be smaller than the minimum line width W_(min). That is, the target line width W_(p2) may be equal to, or may be larger than, the minimum line width W_(min). When the target line width W_(p2) is larger than the minimum line width W_(min), it is possible to obtain an increased lithography margin corresponding to a difference quantity from the minimum line width W_(min) and the resizing quantity ΔL₂ in the first resist pattern 34 a.

Moreover, the target space width S_(p3) does not need to be smaller than the minimum space width S_(min). That is, the target space width S_(p3) may be equal to, or may be larger than, the minimum space width S_(min). When the target space width S_(p3) is larger than the minimum space width S_(min), it is possible to obtain an increased lithography margin, according to a difference quantity from the minimum space width S_(min), and the space width reducing quantity ΔL₂ by the overcoat method, in the second resist pattern 35 a.

[First Modification]

A method for forming a pattern according to a first modification of the second embodiment of the present invention is different from the method for forming a pattern according to the second embodiment in that a TF process utilizing a thermal plastic deformation characteristic of a resist is used as shown in FIGS. 44A to 45, instead of the overcoat method shown in FIGS. 38 to 41.

(a) By subjecting the second resist pattern 35 b shown in FIGS. 37A and 37B to heat treatment, a second resist pattern 35 c is delineated which has window portions 36 i, 36 j, 36 k, and 36 l as shown in FIGS. 44A and 44B. The window portions 36 i and 36 j are obtained by isotropically reducing the window portions 36 e and 36 f, respectively, each by a space width reducing quantity ΔL₂ (=ΔD₂) and each have a side with a length of the target space width S_(p6) in the Y-axis direction. The window portions 36 k and 36 l are obtained by isotropically reducing the window portions 36 g and 36 h, respectively, each by ΔL₂. Note that it is possible to control the space width reducing quantity ΔL₂ by which the window portions 36 e, 36 f, 36 g, and 36 h of the second resist pattern 35 b are reduced through the TF process, by controlling temperature during the heat treatment, duration thereof, the thickness of the second resist pattern 35 b, and the like.

(b) Next, as shown in FIG. 45, thin line portions 33 v and 33 w and connection portions 33 g and 33 h of the underlying mask pattern 33 c are divided respectively, by removing part of the underlying mask pattern 33 c selectively with second resist pattern 35 c as an etching mask, by RIE. Consequently, an underlying mask pattern (isolation pattern) 33 d is delineated. The second resist pattern 35 c is removed by using a resist remover. Since other procedures which are substantially the same as the procedures shown in FIGS. 11, 31 to 37B, and 42 to 43B, repeated description is omitted.

According to the first modification of the second embodiment of the present invention, when the TF process shown in FIGS. 44A to 45 is adopted instead of the overcoat method shown in FIGS. 38 to 54, it is also possible to delineate the process-target film patterns 32 a, 32 b, 32 c, and 32 d having both the line width W_(p2), which is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system, and the space width S_(p6), which is smaller than the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system.

[Second Modification]

As shown in FIG. 46, a method for forming a pattern according to a second modification of the second embodiment of the present invention is different from the method shown in FIG. 1 in that an auxiliary underlying mask film 91, a first anti-reflection film 93, and an anti-reflection film 95 is deposited.

(a) A gate oxide film (first insulator) 31 a, a process-target film 32 made of polycrystalline silicon or the like, and an auxiliary underlying mask film (third insulator) 91 are sequentially deposited on a semiconductor substrate 31 shown in FIG. 46 by CVD or the like. The material of the auxiliary underlying mask film 91 is selected depending on an underlying mask film; for example, the auxiliary underlying mask film 91 is a silicon nitride film (Si₃N₄ film). That is, an underlying mask film (second insulator) 33 which has a higher etching rate than that of the auxiliary underlying mask film 91 is deposited on the auxiliary underlying mask film 91 by CVD or the like. For the underlying mask film 33, when the auxiliary underlying mask film 91 is a nitride film, a silicon oxide film (SiO₂ film) can be selected, for example. That is, a combination of the materials of the auxiliary underlying mask film 91 and the underlying mask film 33 are selected so that the etching rate of the underlying mask film 33 is, e.g., about 10 to 1000 times as high as the etching rate of the auxiliary underlying mask film 91.

(b) Next, a first anti-reflection film 93 is deposited on the underlying mask film 33 by vacuum evaporation, sputtering, or the like. Subsequently, a first resist film 34 is spin-coated on the first anti-reflection film 93. Thereafter, a second anti-reflection film 95 is deposited on the first resist film 34 by vacuum evaporation, sputtering, or the like. For the material of the first and second anti-reflection films 93 and 95, it is possible to use organic translucent resin or the like capable of being spin-coated. Apart from this, it is possible to use an inorganic material, such as a silicon oxynitride (SiON) or a titanium oxide (TiO), capable of being deposited by CVD.

(c) Next, the first mask 40 shown in FIG. 31 is mounted on an unillustrated projection exposure system, and then the pattern of the first mask 40 is transferred onto the first resist film 34 through the second anti-reflection film 95. At this time, a complex refractive index (whose real component corresponds to a refraction index (n), and whose imaginary component corresponds to an extinction coefficient (k)) at the exposure wavelength are adjusted by the first anti-reflection film 93, whereby the reflectance of the exposure light can be controlled. Moreover, variation of the line width due to the influence of the bases such as the underlying mask film 33 can be prevented by the second anti-reflection film 95. Thereafter, the first resist film 34 is developed, and thus a first resist pattern 34 c with the line width W_(p1) is formed as shown in FIG. 47. The first and second anti-reflection films 93 and 95 are patterned into the same shape as the first resist pattern 34 c.

(d) Next, parts of the underlying mask film 33 are selectively removed by RIE or the like, using the first resist pattern 34 c, and the patterned first anti-reflection film 93 and the patterned anti-reflection film 95 as etching masks. Consequently, as shown in FIG. 48, an underlying mask pattern (isolation patterns) 33 d is delineated. The first resist pattern 34 c, the first anti-reflection film 93 and the anti-reflection film 95 are removed by using a resist remover. Since the procedures after the above step is substantially the same as procedures shown in FIGS. 36 to 41, repeated description is omitted.

(e) Next, as shown in FIG. 50, parts of the auxiliary underlying mask film 91 are selectively removed by using hot phosphoric acid or the like, using the underlying mask pattern 33 d as an etching mask. Consequently, an auxiliary underlying mask pattern 91 a is delineated. Then, parts of the process-target film 32 are selectively removed by RIE or the like, using the auxiliary underlying mask pattern 91 a and the underlying mask pattern 33 d as etching masks. Consequently, four process-target film patterns 32 a, 32 b, 32 c, and 32 d (the process-target film patterns 32 k and 32 l are unillustrated) are delineated. The auxiliary underlying mask pattern 91 a and the underlying mask pattern 33 c are removed by use of corresponding etching liquids.

According to the second modification of the second embodiment of the present invention, it is possible to delineate the process-target film patterns 32 a, 32 b, 32 c, and 32 d having both the line width W_(p2) which is smaller than the minimum line width W_(min) with which a pattern can be optically resolved by a projection exposure system, and the space width S_(p6) which is smaller than the minimum space width S_(min) with which a pattern can be optically resolved by a projection exposure system.

Furthermore, by using the first anti-reflection film 93, it is possible to adjust a complex refractive index of a wavelength of exposure, and thus the reflectance of exposure light can be prevented. Furthermore, by using the anti-reflection film 95, it is possible to prevent change of line width by the underlying mask film 33 or the like.

Furthermore, since the auxiliary underlying mask film 91 is used, it is possible to slim the underlying mask pattern 33 d by over etching (slightly etching) the underlying mask film 33, using the auxiliary underlying mask film 91 as an etching stop layer when an etching selectivity is not insufficient between the auxiliary underlying mask film 91 and the process-target film 32. In this case, it is also possible process to the process-target film 32 using the underlying mask pattern 33 c and the auxiliary underlying mask pattern 91 a. Note that a silicon nitride (Si₃N₄) film or the like which is not etched by a oxide etchant may be used as the auxiliary underlying mask film 91 when the underlying mask film 33 is a oxide film, and the underlying mask film 33 is to be slightly etched using a etching liquid for etching the oxide film.

(Other Embodiments)

In the methods for generating mask data according to the first and second embodiments of the present invention, the space width S_(p3), by which the thin line portions 112 a, 112 b, 112 c, and 112 d shown in FIG. 2 are separated from each other, may be different from the space width S_(p3), by which the rectangular portions 111 a, 111 b, 111 c, and 111 d are separated from each other. Furthermore, Various types of design data having various types of shapes and dimensions can be adopted, in addition to the design data 110 and 120 shown in FIG. 2. For example, the thin line portions 112 a and 112 b may be swerved each other in the Y-axis direction, if facing ends of the thin line portions 112 a and 112 b are separated from each other by the space width S_(p3). Furthermore, the thin line portion 112 a and 112 b do not have striped-shapes.

Furthermore, the design patterns 110 a, 110 b, 110 c, and 110 d shown in FIG. 2 which are equally enlarged, may have thin line portions 112 a, 112 b, 112 c, and 112 d enlarged in the Y-axis direction only. Furthermore, in methods for forming a pattern according to the first and second embodiment of the present invention, the first resist patterns 34 a and 34 c are equally reduced, the thin line portions 34 p and 34 q may be reduced in only the Y-axis direction, based on a method of generating mask data.

Furthermore, the positive OPC patterns 143 a, 143 b, 143 c, and 143 d, the negative OPC patterns 144 a and 144 b, and the negative patterns 161 a, 161 b, 161 c, and 161 d shown in FIGS. 6A and 6B are added in order to prevent changing the shapes of patterns on a wafer by optical proximity effects in exposure process, and so that the shapes of the patterns transferred correspond to the patterns of the first mask data 130 and the second mask data 150. Thus shapes and positions of OPC patterns are not limited.

Furthermore, sets of masks according to the first and second embodiment of the present invention, the first mask patterns 11 and 41 and the second mask patterns 21 and 51 are explained as examples only and shapes of a first mask pattern and a second mask pattern are not limited. For example, even though stripe-shaped thin line patterns 11 a and 11 b are explained, thin line patterns do not need to have a stripe-shape. Furthermore, the positive OPC patterns 13 a, 13 b, 13 c, and 13 d, and the negative patterns 14 a, 14 b, 23 a, 23 b, 23 c, and 23 d, are patterns for correcting the shapes of the mask patterns placed on the first and second masks 10 and 20 in order to prevent optical proximity effects when the patterns of the first mask 10 and the second mask 20 are transferred and to obtain desired patterns on a semiconductor substrate. Therefore, the shapes of OPC patterns, and the shapes of mask patterns on which OPC is performed are not limited. That is, the shapes of patterns after OPC can be change by conditions of exposure processes.

Furthermore, in the OPC process according to the first and second embodiment of the present invention, OPC patterns may be generated by hand or the so-called OPC tools. Furthermore, sub-resolution assist features (SRAF) and resolution enhancement technology (RET) such as an alternating phase shift mask may be used to obtain the shapes of patterns on a wafer corresponding to the shapes of the patterns of the first and second masks 130 and 150.

Furthermore, in a method for forming patterns according to the first and second embodiments of the present invention, negative resist films can be used as the first resist film 34 and the second resist film 35 instead of positive resist film. The relationship of permeate and shade of the mask patterns 11 and 41 of the first masks 10 and 40, and window portion of the second masks 20 and 50 may be reversed when a negative resist film is used. As the underlying mask film 33 shown in FIGS. 11 and 46, and the auxiliary underlying mask film 91, silicon oxide (SiO₂), silicon hydroxide (SiO_(x)H_(y)), amorphous silicon, poly-silane, titanium oxide (TiO₂), titanium nitride (TiN), tungsten silicide (WSi), tungsten (W), and novorack resin cured by electron beam or ultraviolet (UV) ray, and the like can be used instead of silicon nitride (Si_(x)N_(y)) and silicon oxide nitride (SiO_(x)N_(y)).

Furthermore, in a method for forming a pattern according to the first embodiment of the present invention, the auxiliary underlying mask film 91 shown in FIG. 46 may also be deposited between the process-target film 32 shown in FIG. 11 and the underlying mask film 33. In a method for forming a pattern according to the second embodiment of the present invention, another plurality of auxiliary underlying mask films, which has a sufficient ratio of etching selectivity to the auxiliary underlying mask film 91 can be deposited under the auxiliary underlying mask film 91 shown in FIG. 46. In the procedure shown in FIG. 46, only one of the first anti-reflection film 93 and the anti-reflection film 95 may be deposited.

Moreover, it is possible to form the mixed layer 62 a including the window portions 63 a, 63 b, 63 c, and 63 d having a side with the target space width S_(p6) by an overcoat method after a TF process for reducing the window portions of the second resist pattern 35 b, instead of using the overcoat method shown in FIGS. 38 to 41 and the example of using a TF process shown in FIGS. 44A and 45 are explained.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof. 

1. A set of masks for forming a thin line portion having a line width thinner than a minimum line width which can be optically resolved by a projection exposure system by slimming a line width of a pattern transferred on a semiconductor substrate, the set of masks comprising: a first mask having a thin line pattern for forming the thin line portion; and a second mask having a window portion for separating the thin line portion on the semiconductor substrate transferred by the first mask so as to have a minimum space width with which a pattern can be optically resolved by the projection exposure system between the separated parts of the thin line portion, wherein the minimum space width is perpendicular to the slimmed line width of the thin line portion.
 2. The set of masks of claim 1, wherein the first mask has a plurality of thin line patterns arranged parallel to one another for forming a plurality of thin line portions on the semiconductor substrate respectively; and the second mask has a plurality of window portions for separating the thin line portions transferred by the first mask respectively. 